Vitamin D2 and vitamin D3 represent the most common sources of vitamin D used in the supplementation of mammals and birds. Vitamin D3 is known to undergo side chain modifications ultimately leading to cleavage at C23/C24 to form the C23 acid excretory product. However little is known with regard to side chain metabolism of vitamin D2. Some preliminary evidence suggests that the vitamin D2 side chain may become saturated at C22 and demethylated at C28, with subsequent metabolism in a similar fashion to vitamin D3. These experiments will lead to a better understanding of the differences between vitamin D2 and D3 metabolism in mammals and birds and may suggest specific therapies. We are therefore proposing the synthesis of 9,11[3H]-25-hydroxyvitamin D2 and 9,11[3H]-1,25-dihydroxyvitamin D2 to investigate side chain metabolism of these two major circulating forms of vitamin D2. User Number: 1606 Tritiation City, State: Ames, IA HPLC Funding Source: USDA NMR Charge: $5799.58 5 days Program Income: $5560.00 (estimated) 2 compounds